Andy Roddick of the United States celebrates match point during his men's singles third round match against Fabio Fognini of Italy. Photo: Getty Images

Channeling his inner Jimmy Connors, Andy Roddick pounded a forehand passing shot down the line to win a 20-stroke point and thrust both arms overhead, motioning to the U.S. Open spectators to make more noise.

Moments later, Roddick hit a volley into an open court and chugged back to the baseline, wagging his right index finger.

Yes, Roddick is having a grand ol’ time at his retirement party — and he’s not done yet.

Winning a second consecutive match since announcing the U.S. Open will be the last tournament of his career, 2003 champion Roddick stuck around at least a little longer by getting past 59th-ranked Fabio Fognini of Italy 7-5, 7-6 (1), 4-6, 6-4 in the third round Sunday.

“I’m trying to keep my emotions together, all the while trying to appreciate this tournament. You guys have just made it so special,” Roddick told the fans during an on-court interview at Arthur Ashe Stadium. “I’m just enjoying it. I love this place, and I love all of you, and I’m having a blast.”

In the fourth round Tuesday, the last American man to win a Grand Slam title will face 2009 U.S. Open champion Juan Martin del Potro, who needed six match points to defeat Leonardo Mayer 6-3, 7-5, 7-6 (9). That 20-point tiebreaker included a backhand by Mayer that somehow ricocheted off the top of a net post and landed on the court.

It was last Thursday, Roddick’s 30th birthday, that he surprisingly let the world know he had decided to walk away from the sport whenever this visit to Flushing Meadows ends.

Sunday just so happened to be five-time U.S. Open champion Connors’ 60th birthday — and on the very same date in 1991, Connors celebrated his 39th by coming back to beat Aaron Krickstein in five sets to reach the quarterfinals in New York, a match replayed often during rain delays in more recent times. Connors, who briefly coached Roddick, was at his rabble-rousing, crowd-goading best on that day 21 years ago, and the pupil provided a more muted rendition this time.

Fognini got in on the act, too, helping make things rather entertaining.

Set aside that Fognini broke Roddick to end the third set and force a fourth. Fognini is a real character, too, and he conjured up one tremendous, full-sprint, back-to-the-net, between-the-legs shot; after Roddick replied with a stretch volley winner into the open court to end the point, Fognini chucked his racket all the way to the service box.

There was more, including when Fognini stuck his mug right up against a TV camera after one point; requested instant-replay challenges of two faults on another (both serves were, indeed, out); and kept up a stream of sailor-language muttering in Italian.

Part of Roddick’s appeal, in addition to an ability to play tennis well enough to reach five Grand Slam finals and get to No. 1 in the ATP rankings, is his showmanship and quickness with a quip.

Dealing with a series of injuries over the past few seasons, including a pinched and painful right shoulder, Roddick dropped out of the top 20 in February, then slid to No. 34 in March, his lowest ranking since 2001. A balky right hamstring forced Roddick to retire during his second-round match at the Australian Open in January, and he lost in the first round at the French Open and third round at Wimbledon.

The 20th-seeded Roddick certainly won’t be favored against No. 7 del Potro. But Roddick is into the fourth round for the ninth time in 13 appearances in the U.S. Open, and he’s 8-0 so far.

There were moments when Roddick appeared sluggish Sunday, and his big serve — he once owned the record for fastest, at 155 mph — wasn’t always what it can be. Fognini, who at 5-foot-10 is four inches shorter than Roddick, actually wound up with more aces, 15 to 10.

But the key moment came in the second-set tiebreaker. Fognini took the first point; Roddick the rest.

At 1-all, Roddick really came alive, as did the partisan crowd, when he smacked a winner and gestured vigorously. He followed that with a pair of aces at 126 mph and 131 mph and pretty much was on his way.

There was the third-set blip, of course, but otherwise Roddick stayed steady, breaking Fognini twice in a row in the fourth and raising his clenched right fist overhead after going up 4-3.

After Fognini missed a backhand return on match point, Roddick rolled his head back and raised both arms overhead, then swatted a ball into the stands. The pair of pals met at the net, and Fognini pulled Roddick in for a hug.

Roddick answered the fans’ standing ovation with one of his own, clapping overhead while standing near the middle of the court. When he sat in his changeover chair, Roddick exhaled a couple of times, taking it all in. As Fognini strode past on his way back to the locker room, he paused to slap palms with Roddick.

“It doesn’t really matter how much energy I have,” Roddick said. “You just keep going. I’m going to give it my all here.”